Marks Daily Apple
Serving up health and fitness insights (daily, of course) with a side of irreverence.
10 Mar

Dear Mark: Is a High Protein Diet Really As Bad for You As Smoking?

SteakIt’s about that time, boys and girls. A new “protein kills” study has arrived to throw you into the pit of existential angst and self-doubt you recently managed to crawl out of from the last one. As you may know, I’ve just spent a week in Tulum, Mexico for PrimalCon (which was amazing, by the way, absolutely fantastic) where I managed to avoid most contact with my inbox. Oh, I took a couple glimpses here and there, enough to notice an endless stream of frenzied email subject lines, but I didn’t read the contents until the flight home. I still knew what was coming.

I finally have a little time to dig into this paper (which actually covers two studies) to see if there’s anything we can learn. Let’s jump right in…


A co-worker informed me of a news clip she’d heard regarding an increased cancer risk for those who stick to a high animal protein-based diet. She said that smoking cigarettes is healthier than eating high fat/high protein diet. My first reaction was to chuckle (just another CW media attack against Paleo/Primal) and I did once I read the actual piece in Forbes. I wanted to get your thoughts on it as a lot of the article’s evidence once again seems inconclusive. Seems like there are a lot of caveats.


Right off the bat, we can read the paper and see an important part that the journalists conveniently left out:

Conversely, high protein intake was associated with reduced cancer and overall mortality in respondents over 65, but a 5-fold increase in diabetes mortality across all ages.


Using Cox Proportional Hazard models, we found that high and moderate protein consumption were positively associated with diabetes-related mortality, but not associated with all-cause, CVD, or cancer mortality when subjects at all the ages above 50 were considered.

Huh. From age 50-65, protein modestly increases mortality, especially cancer- and diabetes-related mortality. In ages 50+, though, a high protein intake has no association with all-cause mortality (the most important endpoint), while in ages 65+, high protein is downright protective. The only consistent positive association across all ages is with diabetes mortality. How can this be?

It’s well known that seniors are less efficient at utilizing protein than younger people. Muscle protein synthesis is slightly impaired in the elderly, for example. As such, they need to eat more of it to get the same benefits as the rest of the population. It may be that they also have a higher upper threshold for protein until harm ensues – a higher “protein ceiling.”

Other populations also have higher ceilings. Runners, cyclists, dancers, swimmers, weight lifters (especially weight lifters) all need more protein than the sedentary, just like the seniors. Unfortunately, the authors did not control for exercise. Too bad, because it probably would have modified the relationship between protein intake and mortality in the other age groups.

I think if anything can be taken from this study, it’s that you should only eat as much protein as you require. We likely all have “safe protein ceilings” depending on various factors, like age and activity level. The ceiling is higher the older and more active you are.

Since the connection between diabetes-related mortality and protein persisted even among the older crowd, let’s look at that a little further. Does other research agree that protein is bad for diabetics?

Well, in the most recent meta-analysis dealing with diet and diabetes, researchers concluded that “low-carbohydrate, low-GI, Mediterranean, and high-protein diets are effective in improving various markers of cardiovascular risk in people with diabetes and should be considered in the overall strategy of diabetes management.” They looked at both epidemiology and clinical trials to reach that conclusion, so it’s not clear how protein is increasing diabetes mortality in the current study if the relationship is causal.

I’m not suggesting that you eat all the protein you want as long as you’re exercising or elderly. I’ve even softened my “high-protein” leanings over the years, advocating instead for a more moderate approach. One gram protein per pound of lean tissue is plenty for most active people, and many can get by on half that.

The Mouse Study

Okay, that’s one part of the paper. There was also a study that found both breast cancer and melanoma tumors grew more slowly in mice on a 4-7% protein diet than mice on an 18% protein diet. High protein mice also had higher levels of IGF-1, a growth promoter, and the rate of tumor growth was associated with the amount of IGF-1 secreted. The protein was entirely casein, with a touch of added methionine.

When I saw that they used casein, it reminded me of something from Chris Masterjohn’s analysis of the T. Colin Campbell casein/cancer studies. While high intakes of casein promoted the growth of existing tumors in those rodents, it was also protective against the mutagens that cause the initial appearance of tumors. Protein was protective against cancer until they had it, at which point it accelerated the cancer’s progression. Rodents on the low protein diet were more susceptible to getting cancer after aflatoxin exposure. Once the rodents already had cancer, low protein was protective against further growth.

Does this phenomenon apply to the most recent study? Impossible to tell. The mice were directly injected with melanoma and breast cancer cells, not exposed to a cancer-causing toxin or exposed to high levels of UV radiation. This usually isn’t how cancer develops in the real world, unless we’re talking about mistakenly receiving a cancerous organ transplant. We tend to develop cancer in response to mutagens in the environment.

That said, we can’t discount the results entirely. Getting your protein only from casein is unwise (and unfeasible when eating whole foods). Methionine (an amino acid common in muscle meat which does increase IGF-1) probably should be balanced with glycine (an amino acid common in connective tissue and gelatinous cuts of meat). I think glycine is especially important for a few reasons:

Realize that the Primal eating plan doesn’t prescribe “eating lots of meat.” Instead, we “eat animals,” and animals have bones and gristle and organs and tendons and loins and ribs and shoulders and all kinds of edible bits and pieces with extremely varying amino acid profiles. Over the years, I’ve been emphasizing these “alternative” cuts more and more. The folks profiled in the study’s data sets probably weren’t eating whole animals. The mice definitely weren’t. We largely just eat meat, and I think that should probably change if we want to maintain optimal health and avoid some of the diseases the epidemiology keeps pointing at.

There are also untoward effects of ultra-low protein intakes to consider. While this paper was only concerned with the cancer endpoint, free-living, free-thinking, autonomous humans with hopes, desires, aspirations, and goals aren’t only worried about cancer. We’d certainly prefer not to have cancer, but what if the narrow pursuit of the ultimate anti-carcinogenic diet has unpleasant side effects that affect the enjoyment of our lives?

Consider that low protein diets:

In other words, starving yourself of protein (the mice in the study achieved the protective effects by eating just 4-7% of calories as protein, which qualifies as protein starvation in most books) may reduce tumor growth, but it might make you fatter and weaker, give you brittle bones, prevent you from taking care of yourself in the later years, and make you more susceptible to illness. Oh, and it may even make you more vulnerable to initially getting cancer (if the Campbell casein studies are applicable to people). But that’s all worth it if once you have cancer the tumors grow slightly more slowly, right?

Even IGF-1 isn’t evil. It promotes growth across the board – in muscles and in tumors. Tumors suck, but not everyone has tumors. Everyone does have muscles. IGF-1 secretion also promotes neural growth and resistance to neurological degeneration. In a study mentioned in yesterday’s Weekend Link Love, elderly women improved muscular and cognitive function by eating a diet high in protein derived from red meat and lifting heavy things. Another study found that increased IGF-1 was linked to improved memory and vigor in both middle-aged and elderly subjects. I don’t know about you, but “living long and dropping dead” is all about vigor for me.

Think about it. Vigor. Sure, it’s not exactly a traditional health biomarker, but who’s got it? What kind of older people display vigor?

The sassy centenarian who eats bacon for breakfast every single day.

The old guy with the vise-grip for a handshake.

That old dude surfing with all the guys a third his age.

The 85 year-old great grandmother who shoulders past you at the farmer’s market to get the best leeks.

The old lady who beats you at raquetball.

I will take vigor every single time even if it modestly increases the speed of tumor growth on the off chance I get cancer. That’s just me, though.

Summing Up

As I see it, there are some potential takeaways, keeping in mind that half the paper was based on epidemiology:

Don’t eat more protein than you actually need. Get extra calories from fat and, if activity warrants it, carbs.

Eat the whole animal. Don’t just eat muscle meat, but also bones, ligaments, shanks, cartilage, tails, and organs. Supplementary gelatin is a good idea if you don’t eat the aforementioned foods.

Don’t eat a diet of casein, methionine, soybean oil, corn starch, and sucrose, especially if you have cancer.

And some questions:

High IGF-1 levels are linked to bad things like cancer, but also good things like strong muscles and a sharp mind. How do we balance the two?

Were processed meat and fresh meat lumped together? Is pepperoni pizza “meat”?

What about people younger than 50? They weren’t addressed at all.

How valid is the dietary data? It was gathered by calling people on the phone and asking them what they’d eaten the previous day and whether that was typical of their normal diet. Seems awfully unreliable and prone to human error.

That’s my take. There are many others out there, but this is mine. What do you think?

You want comments? We got comments:

Imagine you’re George Clooney. Take a moment to admire your grooming and wit. Okay, now imagine someone walks up to you and asks, “What’s your name?” You say, “I’m George Clooney.” Or maybe you say, “I’m the Clooninator!” You don’t say “I’m George of George Clooney Sells Movies Blog” and you certainly don’t say, “I’m Clooney Weight Loss Plan”. So while spam is technically meat, it ain’t anywhere near Primal. Please nickname yourself something your friends would call you.

  1. Thanks Mark for your comments on this recent study.
    My simple take is that I need to balance protein with fats and plenty of vegies. No change there.
    And, be as active as possible. No change there.

    Geoff McDonald wrote on March 11th, 2014
  2. The study was torn apart pretty much but it got huge media coverage with it’s sensationalistic headline ‘more dangerous than smoking’

    Dr John Briffa did a great piece

    and before him Zoe Harcombe

    It got people talking. That’s for sure. I eat a lot of protein, but i also eat lots of vegetables and the food sources are clean and unprocessed…..BUT do I smoke, do I work out – what’s the control group etc?

    Jo Baxas wrote on March 11th, 2014
  3. Didn’t take any notice of this article when it first came out. Setting aside smoking, alcohol etc. I firmly believe that the way we work has a greater impact (long term) on our health than eating meat – by that I mean sitting behind a screen at work and then sitting behind another screen when we get home (TV, iPad, phone).
    Agree with Mark on vigour – just taken up boxing at the age of 63 and can’t believe the level of stamina I seem to have.
    When I read that the likes of Sir Steve Redgrave (UK 6 times Olympic gold medallist – rowing) and Sir Ranulph Fiennes (worlds best known explorer – Everest, North Pole) both suffer from Type II because of all the chocolate, cakes and biscuits they’ve wolfed down over the years I think I’ll take the risk with meat

    Paul and Karen wrote on March 11th, 2014
  4. Again it’s been proved that one need to eat balanced diet, eating protein or vitamins excessively can negatively affect your health. So always focus on eating all nutrients.

    Bharat wrote on March 11th, 2014
  5. I was vegan (I know, I know) for a few months and I felt so awful! My doctor finally told me to start eating meat again because I had no energy whatsoever. Just thought I would share how eating more protein has made me feel healthy.

    Ray wrote on March 11th, 2014
  6. “Don’t eat a diet of casein, methionine, soybean oil, corn starch, and sucrose, especially if you have cancer.”

    Sage advice right there. Nice work Mark.

    BW wrote on March 11th, 2014
  7. A lot of these “studies” that are popping up are reaching. Since industrialization and with the growing affluence of the west, people have been looking for validation in taking the easy way out, and getting more unhealthy because of it. Being properly healthy takes a lot of hard work, discipline and commitment. Naturally, folks will try and justify why working hard, being disciplined and committed are not the way to go.

    I’ll take my chances on rate of tumor growth at 65. They can have their COPD, CVD, Diabetes, Acne, IBS, and Gout.

    Charles wrote on March 11th, 2014
    • Best big picture point regarding this subject!!

      victor wrote on March 11th, 2014
  8. nice work Mark and everyone for commenting and exposing this so-called study. i would only add a potential conflict of interest issue that hasn’t been raised by others. namely, four of the paper’s authors are research team leaders or sit on the board of advisors of a company called l-nutra, see

    from their website, they seem extol the benefits of fasting, which is fine enough, but are also developing supplements aimed at obese or recovering patients. they don’t give a lot of details about the make up of the products, but the description of one of them, prolon, is telling ( L-Nutra has developed ProLon™2, which is a proprietary all natural product produced from vegetables (not animals) to achieve a source of all the important vitamins, minerals and other essential micronutrients provided in a balanced form that optimizes absorption and nourishment as a highly nutrition diet would achieve… Prolon™1 and 2 are proprietary, solely plant-based products, comprised of vegetable medleys, broths, energy drinks, teas, and nutrition bars

    Mike_from_UK wrote on March 11th, 2014
  9. Yes they are right! A high protein diet is far deadlier than smoking as it requires far more cows to die to sustain the diet! 😉

    Corina wrote on March 11th, 2014
    • Well, the cows are not smoking so being a protein source would prove to more deadly than smoking for them. 😉

      2Rae wrote on March 11th, 2014
      • Yeap, that is what I meant! But in essence if you look purely at the conclusion, the protein diet is deadlier than smoking so they are right. (The fact that is deadlier for the cows is just a “minor detail” for the researchers! 😉 )

        Corina wrote on March 11th, 2014
        • I wonder what the next step in improving cow farming is.. giving them pasteurized skim milk?

          Animanarchy wrote on March 11th, 2014
  10. Thanks for clearing the air about this study, it is pretty amazing to see so many people go crazy about different studies and then to find out how they get their info! I don’t really get how a study can expect to be taken really serious with such unreliable sources of information. Asking someone what they ate yesterday? They might as well as what I ate last year, because I will never remember!

    Tanner Farenik wrote on March 11th, 2014
  11. Surely this study says that middle-age people should eat MORE protein?

    It says that there is a relationship between the protein that you ate 18 years ago and your current health. If you are 50-65, the ‘effect’ of protein is bad, if you are 65+ the effect is good.

    Most people have taken away from this that people should eat less protein during middle age (ie 50-65). But surely people should start eating more protein 18 years before they hit 65, ie from age 47… ?

    Scott UK wrote on March 12th, 2014
  12. Also quite interesting, the main author of this study, Valter Longo:

    “The study claims to have adjusted for protein in general vs. animal protein to conclude that animal protein is the harmful factor and not protein per se. Call me suspicious, but I always check for conflicts of interest and the lead researcher, Dr Longo, has declared interests in (actually, he’s the founder of) L-Nutra – a company that makes ProLon™ – an entirely plant based meal replacement product.”

    Markus wrote on March 12th, 2014
  13. The Mongols being nomads had a red-meat based diet with hardly any vegetables and they managed to conquer 5/6 of then known world. It’s got tell us something.

    Danny wrote on March 12th, 2014
  14. There are so many comments now, not sure anyone will ever see this. There are several websites I read everyday, including this one. Last Word on Nothing I find interesting and this is what was posted today.

    Had to smile….

    David wrote on March 12th, 2014
  15. I believe factory, feed lot beef and cured deli meats were included in the studies. That seems to be the case when there are studies undertaken regarding protein. In some peoples eyes (research included) all meats are lumped together under the heading of protein when the difference and benefits of grass fed and finished proteins are a night and day difference.

    You can clearly benefit by moving away from refined carbs, sugars and starch to more protein centered but then move all the way to grass fed and finished proteins to complete the transition.

    jamie wrote on March 12th, 2014
  16. They tested a high protein diet on an herbivore?

    Al wrote on March 12th, 2014
  17. Hi folks. Don’t waste your time with this rubbish made just to sell papers

    Rafael wrote on March 13th, 2014
  18. Achieving a protein intake of 4-7% of calories would be difficult on even a vegan diet. Even a vegan diet will typically provide about 10% or more of calories from protein, unless it consists almost exclusively of vegetables, fruits, and nuts and almost eliminates grains and legumes.

    Michael wrote on March 14th, 2014
  19. My question is if you are over 50 and all your health markers indicate no problems (lipid profile, CBC, etc…) isn’t that better data than an epidemiological study on age related cohorts? To take it one step further, if your numbers were borderline before subscribing to a “lifestyle” and the numbers got better using it (high carb, low carb I don’t care what diet) wouldn’t it make sense to stay on that course?

    In the engineering field where I work, the general rule of thumb is that specific localized data overrules standardized data. The best data is site specific. So, personally I will continue on my modified Primal lifestyle until I see evidence that MY situation needs to change through quality of life or medical blood work.

    RMF0466 wrote on March 16th, 2014
  20. For anyone who wants a REALLY in-depth breakdown of the issues with this study (especially the flaws in the study design and the methionine/glycine issue), Denise Minger has, as always, done a fantastic job:

    Caitlin Allday wrote on March 19th, 2014
  21. Mark,

    Could you tell us which parts of the animal are highest in glycine?

    Harriet Sugar Miller wrote on December 24th, 2015

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